The system presently in general use for manufacture of corrugated board involves the application of an essentially ungelatinized starch adhesive to the tips of the corrugated medium flutes. This is applied by means of a rotating glue roll running in a pool of the adhesive and transferring the adhesive to the flute tips. The mechanics, chemistry and physical dynamics of the system are described in a reference document entitled Corrugating Adhesives Seminar, published by the National Starch and Chemicals Company, Bridgewater, N.J. (1987). Even though it is almost universally practiced, in order to be operated successfully the present system has some well known problems and sensitivities which must be accounted for. These factors create limitations, or potential limitations in the manufacturing process, especially as to the speed of operation and various product deficiencies such as inconsistency of adhesion of the plies of the board.
Other adhesive application systems have been proposed but these have not received significant acceptance. As one example, Wolvin, et al., U.S. Pat. No. 3,972,763, and Alvensleben et al., U.S. Pat. No. 4,223,633, show a system of placing localized spots of a hot melt adhesive along the flute tips of the corrugated medium by the use of a specially constructed glue roll system. Dooley, U.S. Pat. No. 3,518,142 in FIG. 6, displays a manifold which extrudes a full sheet width ribbon of hot melt adhesive onto the flute tips. The device is presented as an alternative to the use of a transfer roll to apply the adhesive. Hot melt adhesives, as used in Wolvin and Dooley, are relatively expensive and the high cost has greatly limited their use.
Miller, in U.S. Pat. No. 5,316,828 teaches an adhesive system comprising continuous parallel beads of adhesive applied to the corrugated medium transverse to the flutes of the medium. Hot melt adhesives can be used in this application, but are relatively expensive. The customary starch adhesive used for corrugated board has not been fully satisfactory because the adhesive does not hold its shape well, and too much water is conveyed to the board. This tends to cause problems in drying and may cause subsequent warpage.
It is known to heat and cool a melted starch solution within a given processing cycle. As one example, Wittwer et al., U.S. Pat. No. 4,673,438, melt a starch solution and inject it into a mold cavity where it is cooled to solidify the composition into a useful molded part, such as a capsule. Moore, in U.S. Pat. No. 4,913,924, describes manufacture of edible gel pieces of a starch composition. This involves heating the composition to a flowable condition at 290.degree.-340.degree. F. and subsequent cooling to a suitable viscosity for molding. Sair et al., in U.S. Pat. No. 4,232,047 describe manufacture of an encapsulated food additive within a matrix such as starch. A mixture of additive and matrix is heated up to 300.degree. F. or higher with subsequent cooling below 212.degree. F. before exiting the extruder. This eliminates the expansion or "puffing" of the product experienced at higher exit temperatures.